1. Field of the Invention
The instant invention relates to seismic exploration and more particularly to a method for estimating subsurface petrophysical parameters such as porosity from seismic reflection data.
2. Description of the Related Art
Historically, three-dimensional descriptions of hydrocarbon-bearing reservoirs were based primarily on the interpolation between borehole locations of well-log and core analysis data. The well-log data and core analysis were particularly useful in determining at each well location the thickness, porosity and permeability of subsurface units which act as a reservoir for economic fluids, such as oil or gas. Optimum development and production drilling between or away from existing well locations cannot be achieved using the above approach. Often, the costs involved in drilling a well may not be justified when considering the risks involved with a poorly defined subsurface reservoir.
The advent of seismic exploration provided an unparalleled tool for determining subsurface structure. As is generally well known, a seismic signal of limited frequency range may be generated in the earth. A portion of the signal propagates downwardly and is reflected by the structural and lithologic changes in the subsurface. The reflected signals arriving at the surface are detected by sensors coupled to the earth in a predetermined pattern. The early seismic recordings or "seismograms" were crude compared to the records collected today. Despite the great advances in exploration, petrophysical particulars of hydrocarbon reservoirs, such as porosity and permeability, are not detectable using seismic exploration alone. Seismic data only provide a general illustration of the subsurface structure and of gross lithologic and fluid changes.
Of the techniques mentioned above, none have proven to be satisfactory and there remains a longstanding need within the industry for a method to readily determine subsurface structure as well as gross lithologic and fluid changes.